LED dimming control may be utilized to provide control of LED brightness without changing LED color. For example, PWM dimming control uses a PWM signal to drive a LED. FIG. 1 illustrates the PWM dimming control signal, as well as inductor current in the LED driver and LED current controlled by the PWM input signal. The LED current may be programmed for maximum brightness and then “chopped” over a range of duty cycles to achieve a range of brightness levels. The PWM dimming control signal may be applied to the LED through a field effect transistor. When the PWM signal goes low, the LED may be turned off. When the PWM signal goes high, the LED current may return to its previous on state.
The PWM dimming ratio is inversely proportional to the duty cycle (D) of the PWM signal, i.e.PWM dimming ratio=1/D=Tpwm/TpwmON,where Tpwm is a period of the PWM signal, and                TpwmON is PWM pulse width.        
The maximum PWM dimming ratio may be calculated based on the maximum PWM period and the minimum PWM pulse width as follows:PWM maximum dimming ratio=TpwmMAX/TpwmON—MIN,where TpwmMAX is the maximum PWM period, and                TpwmON—MIN is the minimum PWM pulse width.        
As illustrated in FIG. 2, conventional PWM dimming control is provided to enable LED driver operation during the on time of the PWM signal and disable LED driver operation during the off time of the PWM signal. A random delay time Td is created between the active edge of the PWM signal and the starting ramp of the inductor current representing the moment when the power switch driving the LED is turned on. After a time period Tr, the rising inductor current reaches its average value I(L) (ave).
For applications requiring a large range of brightness control, the maximum PWM dimming ratio must be made high. This requires the LED driver to be capable of responding to a very low duty cycle PWM signal. The LED driver must be able to switch from zero inductor current to maximum inductor current during the short time that the PWM input is active. However, the delay Td reduces time available for the LED driver to reach the maximum inductor current. Therefore, a reduced maximum PWM dimming ratio must be used to give the LED driver sufficient time to reach the maximum inductor current.
In addition, as discussed above, the delay time Td is random. The variation in the delay time Td results in the respective LED current variation which can be visible to the human eye as LED flicker.
Therefore, it would be desirable to create a novel PWM dimming control technique to increase the maximum PWM dimming ratio and avoid LED flicker.